I understand all of your arguments, and I understand climate change very well. The problem I keep seeing is not even US fossil fuel consumption so much, it is worldwide fossil fuel consumption. I don't necessarily think the tar sands should be developed, but I think that they will regardless. Unfortunately, the people in charge of economic & environmental issues on both sides of the border are motivated by the money at stake, and that will play huge into the decision. The problem I see is that our opinions don't seem to matter much - even with the protests and public disapproval.
Even if the pipeline is not built, I very much believe the oil will be extracted and exported by Canada, again, because they will want the economic boost that money can provide.
Is this a good idea? Most certianly not, but the sad fact is that governments and policy makers are either not motivated or brave enough - to enact the necessary measures it would take to keep climate change below the 2degree C rise that is the IEA's goal (we could pass that by 2017 easily per the most recent World Energy Outlook)
Germany and other European countries have had success with renewables like solar, but have also had problems like high energy prices, and policy makers in this country won't (in my opinion) want to risk implementing those measures until they believe there will not be any negative impacts.
It would take the entire world implementing radical energy efficiency and emissions policies to keep climate change in check. I would love to see that. But, as an incurable cynic, I see too much arguing among politicans and corporations (who do hold WAY too much clout - you're right) getting in the way of any swift progress. I think we'll cut our addiction to fossil fuels when they run out or cost too much.
If there is a plus side - it would be a step for energy independence for North America - which is a hot topic at the moment as you know. Maybe that helps validate the planned extraction of oil, maybe not. But, it is an issue to be considered alongside the environmental impacts. I think it would be a positive if the oil stayed here because we have environmental policies in place that other countries do not. It's possible (especially if there is a carbon tax added to the mix as you mentioned) that GHG emissions would be lower if the oil is used here than in countries with little or no environmental protections.
So, what I wrote was not really a cheerleading piece for Keystone, but simply a blunt report on what I think is happening.
Thank you for reading! You bring up so great points that are very worthy of serious discussion.